ASP.NET Web PDF Document Viewer/Editor Control Library

function, interpretInt, that queries the expression passed to it to see whether it is an integer. If it is, it prints the value of that integer; otherwise, it prints the string "not an int". #light open Microsoft.FSharp.Quotations open Microsoft.FSharp.Quotations.Typed let interpretInt exp = let uexp = to_raw exp in match uexp with | Raw.Int32 x -> printfn "%d" x | _ -> printfn "not an int" interpretInt 1 interpretInt 1 + 1 The results are as follows: 1 not an int We printed two expressions with interpretInt. The first was an integer value, so it printed out the value of that integer. The second was not an integer, although it contained integers. Quotations are a very big topic, and we can t cover them completely in this section or even in this book. You will, however, return to them in Meta-programming with Quotations in 11.

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//******************************************* // Read the I2C button state and returns button number // The buttons are on lower half of PCF8574 data byte // Rightmost button have priority. int GetButtons() { WriteBuf[1] = 0xff; do { I2CBytes(I2Cport, WriteBuf, RdCnt, ReadBuf); } while (ReadBuf[0] == 0xff) for(int i=0; i<4; i++) { if((ReadBuf[0] & 1) == 0) return i; ReadBuf[0]>>=1; } } task main () { int i; // Configure NXT port SetSensorLowspeed (I2Cport); TextOut(8, LCD_LINE3, "NXT Simon"); TextOut(8, LCD_LINE4, "Press orange"); TextOut(8, LCD_LINE5, "button to start"); // Wait for orange button and seed random generator do { Random(); } while (! ButtonPressed (BTNCENTER, true)) TextOut(8, LCD_LINE4, " "); TextOut(8, LCD_LINE5, " "); Wait(1000); // Initialise notes buffer, without repetition ArrayInit(notes, 0, MaxNotes); int Val=Random(4); notes[0]=Val; for(i=1; i < MaxNotes; i++) { do { Val=Random(4); } while (Val == notes[i-1]); notes[i] = Val; }

Summary

The XMLHttpRequest object provides two properties that provide access to the server response. The first property, responseText, simply provides the response as a string. The second property, responseXML, provides the response as an XML object. Retrieving the response as simple text is fine for simple use cases, such as when the response is displayed in an alert box or the response is a simple one-word phrase indicating success or failure. The previous example in 2 accessed the server response using the responseText property and displayed it in an alert box.

for(i=1; i < MaxNotes; i++) { // Play tune int fail=false; for(int j=0; j<i; j++) { LedTone(notes[j]); } // Check if players correctly reproduce melody for(int j=0; j<i; j++) { int button=GetButtons(); LedTone(button); if(button != notes[j]) { fail=true; break; } } Wait(1000); if(fail) break; } ClearScreen(); TextOut(10, LCD_LINE3, "Game Over!"); TextOut(10, LCD_LINE4, "Level Reached"); NumOut(10, LCD_LINE5, i); PlayTone(TONE_C6, 100); Wait (100); PlayTone(TONE_G5, 120); Wait (120); PlayTone(TONE_E5, 150); Wait (150); PlayTone(TONE_C5, 170); Wait (170); PlayTone(TONE_G4, 200); Wait (5000); } Listing C-4. magicwand.nxc #define I2Cport S1 #define Touch S4 #define Motor OUT_A // I2CAddr8574 = 0x40 for PCF8574 // I2CAddr8574 = 0x70 for PCF8574A #define I2CAddr8574 0x40

In this chapter, you saw how to organize code in F#. You also saw how to comment, annotate, and quote code, but you just scratched the surface of both annotation and quoting. This concludes the tour of the F# core language. The rest of the book will focus on how to use F#, from working with relational databases to creating user interfaces, after you look at the F# core libraries in the next chapter.

Accessing the server response as simple text doesn t provide much flexibility. Simple text lacks structure and is difficult to parse logically with JavaScript. It also makes it more difficult to dynamically generate page content. The responseText property becomes useful if you utilize it in conjunction with the innerHTML property of HTML elements. The innerHTML property is a nonstandard property first implemented by Internet Explorer and later by many other popular browsers. It is a simple string that represents the content between a set of start and end tags.